There are four valves within the human heart that serve to direct the flow of blood through the two sides of the heart in a forward direction. On the left (systemic) side of the heart are the mitral valve, located between the left atrium and the left ventricle, and the aortic valve, located between the left ventricle and the aorta. These two valves direct oxygenated blood coming from the lungs, through the left side of the heart, into the aorta for distribution to the body. On the right (pulmonary) side of the heart are the tricuspid valve, located between the right atrium and the right ventricle, and the pulmonary valve, located between the right ventricle and the pulmonary artery. These two valves direct de-oxygenated blood coming from the body, through the right side of the heart, into the pulmonary artery for distribution to the lungs, where it again becomes re-oxygenated to begin the circuit anew.
All four of these heart valves are passive structures that do not expend any energy themselves and do not perform any active contractile function. They consist of moveable leaflets that are designed simply to open and close in response to differential pressures on either side of the valve. The mitral and tricuspid valves are referred to as atrioventricular valves because of their location between an atrium and a ventricle on each side of the heart. The mitral valve has two leaflets and the tricuspid valve has three. The aortic and pulmonary valves are referred to as semilunar valves because of the unique appearance of their leaflets, which are more aptly termed cusps and are shaped somewhat like a half-moon. The aortic and pulmonary valves each have three cusps.
The three cusps are soft tissue structures attached to a wall of the valve in an area designated as the annulus. In the case of the aortic valve, the three cusps are pushed open against the wall of the aorta during systole (when the left ventricle contracts), thereby allowing blood to flow through. During diastole (when the left ventricle relaxes), the left ventricular pressure falls and the aortic valve cusps reapproximate (the three cusps fall away from the wall and close), thereby preventing the blood which has entered the aorta from regurgitating (leaking) back into the left ventricle.
Heart valves may exhibit abnormal anatomy and function as a result of congenital or acquired valve disease. Problems with heart valve functions can be classified into two categories: 1) stenosis, in which a valve does not open properly, or 2) insufficiency (also called regurgitation), in which a valve does not close properly. Due to the higher-pressure gradient, the mitral and aortic valves are subject to greater fatigue and/or risk of disease. Also, while mitral valves often can be surgically repaired, most abnormalities of the aortic valve require replacement.
Prosthetic heart valves used to replace diseased or abnormal natural heart valves include mechanical devices with, for example, a rigid orifice ring and rigid hinged leaflets or ball-and-cage assemblies, and bioprosthetic devices that combine a mechanical assembly with biological material (e.g., human, porcine, bovine, or biopolymer leaflets).
In the past, heart valve replacement typically required median sternotomy and cardiopulmonary bypass. More recently, various prosthetic heart valves that can be implanted by less invasive procedures have been developed. For example, various replacement heart valve apparatus that can be delivered via an endovascular transcatheter approach are described in co-owned, co-pending U.S. patent application Ser. Nos. 11/052,466 and 60/757,813, the entire disclosures of which are incorporated by reference herein for all purposes. The replacement heart valve apparatus described in these patent applications generally include a compressible valve frame and a compressible docking station that is deployed prior to the introduction of the valve frame into a patient's heart. The valve frame is subsequently positioned within the docking station, which helps to support and anchor the valve frame in the desired location.
Like other transcatheter heart valves that are currently known or available, implantation of the aforementioned replacement heart valve apparatus in the aortic position (as opposed to the pulmonic position) presents unique challenges due to its close proximity to both the mitral valve and the coronary ostia, as well as high systemic pressures and the inability of the body to tolerate free leakage through the aortic valve for any period of time. For example, the implantation of the docking station in the aortic position can require coverage and complete immobilization of the native aortic valve, which will cause free regurgitation. Similar difficulties and challenges, albeit to a slighter extent, can be expected with implanting the replacement heart valve apparatus in other positions, for example, the mitral position, in which case, free regurgitation into the lungs via the left atrium can occur. Acute free regurgitation, even for the short period of time necessary to deliver the valve component within the docking station, is unlikely to be tolerated by the patient, particularly in the target population of patients with pre-existing heart conditions due to stenosis and/or regurgitation. While theoretically, a patient can be put on cardiopulmonary bypass to prevent or reduce such regurgitation, the various health risks associated with a bypass procedure make this an impractical option for many patients in the target population.
The present teachings, therefore, relate to an improved transcatheter heart valve prosthesis adapted to be implanted in the aortic position. However, the present teachings can be adapted for the replacement of other anatomical valves.